This invention pertains to water atomization of metals and more particularly to a method of producing atomized alloy particles containing substantially reduced amounts of metal oxides formed during the water atomizing process.
Water atomization of molten metal alloys is shown in U.S. Pat. No. 2,956,304 wherein metal particles are produced at a particularly small particle size less than 100 mesh. Water atomization of molten metals appears to cause considerable oxidation of certain copper alloy products due to the high temperatures of the molten metal and the oxidizing characteristics of the water itself. High levels of metal oxides increase corrosion as well as decrease compacting properties of metal powders in conventional powder metallurgy. Further, various metal alloys can create an explosion hazard during the water atomization process due to the high level of oxide formation in the alloy particles produced during the water atomization process. Oxidation apparently forms free hydrogen which then tends to form an explosive mixture with oxygen and/or surrounding air. Alloys having considerable affinity for oxygen include for example, copper-manganese, copper-chromium, and copper-zirconium alloys. As the level of oxidation increases, the greater is the chance of explosion. Oxidation depends on the metal melt temperatures and inclusion of preferentially oxidizable metals such as manganese, chromium, and/or zirconium.
It now has been found that the inclusion of minor amounts of silicon within the copper alloy to produce an alloy containing approximately a weight ratio of about 9/1 of oxidazable metal to silicon effectively eliminates the explosion hazard during the water atomization process and further produces an improved copper alloy having a substantially reduced oxide content. The silicon becomes preferentially oxidized rather than oxidazable alloy metal such as manganese, chromium, and zirconium. The minor amount of silicon is believed to diffuse to the surface of individual atomized particles during the water atomization process and to form a protective surface oxide film of the silicon dioxide whereby the alloy metal particles remain in a non-oxidized state. The oxide film appears to eliminate the explosion hazard and provides an improved alloy powder. Powders essentially free of oxides have improved compacting properties, reduce corrosion of the metal alloy particles, and impart superior brazing characteristics.
These and other advantages of this invention will become more apparent by referring to the Detailed Description of the Invention.